Share view context with presenters

This changes the way presenters work in this application so that they
have the equivalent of a view object available to call helpers on. This
removes the need to import specific helpers into individual presenters.

The reason for adding this in is to fix a number of subtle issues that
can occur when it comes to generating URLs without any request
context. This problem affected me when I went to looking at adjusting
the asset host in order to make progress towards RFC-115 [1].

I found that we'd experience different behaviours on asset url methods
depending on the GOVUK_ASSET_ROOT env var. When this env var is not set,
as per [2], any calls for an asset_url would return a path rather than
URL like we requested; when a GOVUK_ASSET_ROOT env var is set as a
hostname without protocol, as per [3], any calls for asset urls would
raise a "undefined method `protocol` for nil:NilClass" exception at [4].
These problems don't affect production since GOVUK_ASSET_ROOT is set as
a full URL.

Anyway, I came to the conclusion that these presenters are effectively
just extensions of the view - evidenced by the high proliferation of
view helpers embedded - and I felt that it'd be easier to have a
view_context object available to call any view helpers we might want.
This helps us out when it comes to rendering asset_urls as this view
context object has the request context available and can determine the
URL based on the request.

Were we to use Rails route helpers for navigating the app we'd also be
able to drop the various usages of Plek.current.website_root and instead
rely on view context to generate URLs.

[1]: https://github.com/alphagov/govuk-rfcs/blob/master/rfc-115-enabling-http2-on-govuk.md
[2]: https://github.com/alphagov/govuk-docker/blob/4b40e479799ea304709276efb29c49898a8b8c9f/projects/government-frontend/docker-compose.yml#L48-L57
[3]: https://github.com/alphagov/govuk-docker/blob/4b40e479799ea304709276efb29c49898a8b8c9f/projects/government-frontend/docker-compose.yml#L20-L30
[4]: https://github.com/rails/rails/blob/92d03850f3bb4c44103d0b06b43e14d6e270e646/actionview/lib/action_view/helpers/asset_url_helper.rb#L303

app/controllers/content_items_controller.rb

@@ -63,7 +63,9 @@ def load_content_item
       content_item["links"]["ordered_related_items"] = content_item["links"].fetch("suggested_ordered_related_items", [])
     end
 
-    @content_item = PresenterBuilder.new(content_item, content_item_path).presenter
+    @content_item = PresenterBuilder.new(content_item,
+                                         content_item_path,
+                                         view_context).presenter
   end
 
   def format_banner_links(links, type)

app/presenters/coming_soon_presenter.rb

@@ -1,7 +1,7 @@
 class ComingSoonPresenter < ContentItemPresenter
   attr_reader :publish_time
 
-  def initialize(content_item, requested_path = nil)
+  def initialize(*args)
     super
     @publish_time = content_item["details"]["publish_time"]
   end

app/presenters/content_item/contents_list.rb

@@ -1,8 +1,5 @@
 module ContentItem
   module ContentsList
-    include ActionView::Helpers::UrlHelper
-    include TypographyHelper
-
     CHARACTER_LIMIT = 415
     CHARACTER_LIMIT_WITH_IMAGE = 224
     TABLE_ROW_LIMIT = 13
@@ -37,7 +34,7 @@ def show_contents_list?
     def extract_headings_with_ids
       headings = parsed_body.css("h2").map do |heading|
         id = heading.attribute("id")
-        { text: strip_trailing_colons(heading.text), id: id.value } if id
+        { text: view_context.strip_trailing_colons(heading.text), id: id.value } if id
       end
       headings.compact
     end

app/presenters/content_item/corporate_information_groups.rb

@@ -9,14 +9,18 @@ def corporate_information?
     def corporate_information
       corporate_information_groups.map do |group|
         {
-          heading: content_tag(:h3, group["name"], id: group_title_id(group["name"])),
+          heading: view_context.content_tag(:h3,
+                                            group["name"],
+                                            id: group_title_id(group["name"])),
           links: normalised_group_links(group),
         }
       end
     end
 
     def corporate_information_heading_tag
-      content_tag(:h2, corporate_information_heading[:text], id: corporate_information_heading[:id])
+      view_context.content_tag(:h2,
+                               corporate_information_heading[:text],
+                               id: corporate_information_heading[:id])
     end
 
     def further_information
@@ -33,7 +37,7 @@ def further_information
 
     def further_information_link(type)
       link = corporate_information_page_links.find { |l| l["document_type"] == type }
-      link_to(link["title"], link["base_path"]) if link
+      view_context.link_to(link["title"], link["base_path"]) if link
     end
 
     def further_information_about(type)
@@ -63,9 +67,9 @@ def normalised_group_links(group)
     def normalised_group_item_link(group_item)
       if group_item.is_a?(String)
         group_item_link = corporate_information_page_links.find { |l| l["content_id"] == group_item }
-        link_to(group_item_link["title"], group_item_link["base_path"])
+        view_context.link_to(group_item_link["title"], group_item_link["base_path"])
       else
-        link_to(group_item["title"], group_item["path"] || group_item["url"])
+        view_context.link_to(group_item["title"], group_item["path"] || group_item["url"])
       end
     end
 

app/presenters/content_item/linkable.rb

@@ -1,7 +1,5 @@
 module ContentItem
   module Linkable
-    include ActionView::Helpers::UrlHelper
-
     def from
       organisations_ordered_by_importance + links_group(%w[worldwide_organisations people speaker])
     end
@@ -38,7 +36,7 @@ def links_group(types)
 
     def organisations_ordered_by_importance
       organisations_with_emphasised_first.map do |link|
-        link_to(link["title"], link["base_path"], class: "govuk-link")
+        view_context.link_to(link["title"], link["base_path"], class: "govuk-link")
       end
     end
 
@@ -56,12 +54,12 @@ def emphasised_organisations
     def link_for_type(type, link)
       return link_for_world_location(link) if type == "world_locations"
 
-      link_to(link["title"], link["base_path"], class: "govuk-link")
+      view_context.link_to(link["title"], link["base_path"], class: "govuk-link")
     end
 
     def link_for_world_location(link)
       base_path = WorldLocationBasePath.for(link)
-      link_to(link["title"], base_path, class: "govuk-link")
+      view_context.link_to(link["title"], base_path, class: "govuk-link")
     end
   end
 end

app/presenters/content_item/national_applicability.rb

@@ -15,7 +15,7 @@ def applies_to
         nations_with_alt_urls = inapplicable_nations.select { |n| n["alternative_url"].present? }
         if nations_with_alt_urls.any?
           alternate_links = nations_with_alt_urls
-            .map { |n| link_to(n["label"], n["alternative_url"], rel: :external, class: "govuk-link app-link") }
+            .map { |n| view_context.link_to(n["label"], n["alternative_url"], rel: :external, class: "govuk-link app-link") }
             .to_sentence
 
           applies_to += " (see #{translated_schema_name(nations_with_alt_urls.count)} for #{alternate_links})"

app/presenters/content_item/no_deal_notice.rb

@@ -1,9 +1,5 @@
 module ContentItem
   module NoDealNotice
-    include ActionView::Helpers::TagHelper
-    include ActionView::Helpers::UrlHelper
-    include ActionView::Context
-
     def has_no_deal_notice?
       content_item.dig("details").has_key?("brexit_no_deal_notice")
     end
@@ -46,7 +42,7 @@ def no_deal_landing_page_cta
         "track-label": "the transition period",
       }
 
-      featured_link = link_to("the transition period", "/transition", data: data_attributes, class: "govuk-link")
+      featured_link = view_context.link_to("the transition period", "/transition", data: data_attributes, class: "govuk-link")
       featured_link_intro = no_deal_notice_links.any? ? "You can also read about" : "You can read about"
 
       (featured_link_intro + " " + featured_link + ".").html_safe

app/presenters/content_item/parts.rb

@@ -1,7 +1,5 @@
 module ContentItem
   module Parts
-    include ActionView::Helpers::UrlHelper
-
     def parts
       raw_parts.each_with_index.map do |part, i|
         # Link to base_path for first part
@@ -86,15 +84,17 @@ def current_part
     def part_links
       parts.map.with_index(1) do |part, position|
         if part["slug"] != current_part["slug"]
-          link_to part["title"], part["full_path"], class: "govuk-link",
-                                                    data: {
-            track_category: "contentsClicked",
-            track_action: "content_item #{position}",
-            track_label: part["full_path"],
-            track_options: {
-              dimension29: part["title"],
-             },
-           }
+          view_context.link_to(
+            part["title"],
+            part["full_path"],
+            class: "govuk-link",
+            data: {
+              track_category: "contentsClicked",
+              track_action: "content_item #{position}",
+              track_label: part["full_path"],
+              track_options: { dimension29: part["title"] },
+            },
+          )
         else
           part["title"]
         end

app/presenters/content_item/title_and_context.rb

@@ -4,7 +4,7 @@ def title_and_context
       {
         title: title,
         context: I18n.t("content_item.schema_name.#{document_type}", count: 1),
-        context_locale: t_locale_fallback("content_item.schema_name.#{document_type}", count: 1),
+        context_locale: view_context.t_locale_fallback("content_item.schema_name.#{document_type}", count: 1),
         average_title_length: "long",
       }
     end

app/presenters/content_item/withdrawable.rb

@@ -1,7 +1,5 @@
 module ContentItem
   module Withdrawable
-    include ActionView::Helpers::TagHelper
-
     def withdrawn?
       withdrawal_notice.present?
     end
@@ -35,7 +33,9 @@ def withdrawal_notice_context
     end
 
     def withdrawal_notice_time
-      content_tag(:time, english_display_date(withdrawal_notice["withdrawn_at"]), datetime: withdrawal_notice["withdrawn_at"])
+      view_context.content_tag(:time,
+                               english_display_date(withdrawal_notice["withdrawn_at"]),
+                               datetime: withdrawal_notice["withdrawn_at"])
     end
 
     def english_display_date(timestamp, format = "%-d %B %Y")

app/presenters/content_item_presenter.rb

@@ -1,10 +1,10 @@
 class ContentItemPresenter
   include ContentItem::Withdrawable
   include ContentItem::NoDealNotice
-  include ApplicationHelper
 
   attr_reader :content_item,
               :requested_path,
+              :view_context,
               :base_path,
               :slug,
               :title,
@@ -19,9 +19,10 @@ class ContentItemPresenter
 
   attr_accessor :include_collections_in_other_publisher_metadata
 
-  def initialize(content_item, requested_path)
+  def initialize(content_item, requested_path, view_context)
     @content_item = content_item
     @requested_path = requested_path
+    @view_context = view_context
     @base_path = content_item["base_path"]
     @slug = base_path.delete_prefix("/") if base_path
     @title = content_item["title"]

app/presenters/document_collection_presenter.rb

@@ -52,7 +52,10 @@ def group_document_links(group, group_index)
   def group_heading(group)
     title = group["title"]
     heading_level = show_contents_list? ? :h3 : :h2
-    content_tag heading_level, title, class: "group-title", id: group_title_id(title)
+    view_context.content_tag(heading_level,
+                             title,
+                             class: "group-title",
+                             id: group_title_id(title))
   end
 
 private

app/presenters/fatality_notice_presenter.rb

@@ -12,13 +12,13 @@ def field_of_operation
   end
 
   def image
-    { "url" => ActionController::Base.helpers.asset_url("ministry-of-defence-crest.png"), "alt_text" => "Ministry of Defence crest" }
+    { "url" => view_context.image_url("ministry-of-defence-crest.png"), "alt_text" => "Ministry of Defence crest" }
   end
 
   def important_metadata
     super.tap do |m|
       if field_of_operation
-        m.merge!("Field of operation" => link_to(field_of_operation.title, field_of_operation.path, class: "govuk-link app-link"))
+        m.merge!("Field of operation" => view_context.link_to(field_of_operation.title, field_of_operation.path, class: "govuk-link app-link"))
       end
     end
   end

app/presenters/gone_presenter.rb

@@ -1,7 +1,7 @@
 class GonePresenter < ContentItemPresenter
   attr_reader :alternative_path, :explanation
 
-  def initialize(content_item, requested_path = nil)
+  def initialize(*args)
     super
     @explanation = content_item["details"]["explanation"]
     @alternative_path = content_item["details"]["alternative_path"]

app/presenters/machine_readable/guide_faq_page_schema_presenter.rb

@@ -1,9 +1,10 @@
 module MachineReadable
   class GuideFaqPageSchemaPresenter
-    attr_reader :guide
+    attr_reader :guide, :view_context
 
-    def initialize(guide)
+    def initialize(guide, view_context)
       @guide = guide
+      @view_context = view_context
     end
 
     def structured_data
@@ -64,11 +65,7 @@ def guide_url
     end
 
     def logo_url
-      image_url("govuk_publishing_components/govuk-logo.png")
-    end
-
-    def image_url(image_file)
-      ActionController::Base.helpers.asset_url(image_file, type: :image)
+      view_context.image_url("govuk_publishing_components/govuk-logo.png")
     end
   end
 end

app/presenters/specialist_document_presenter.rb

@@ -48,7 +48,7 @@ def will_continue_on
 
   def finder_link
     if finder && statutory_instrument?
-      link_to "See all #{finder['title']}", finder["base_path"]
+      view_context.link_to("See all #{finder['title']}", finder["base_path"])
     end
   end
 
@@ -170,7 +170,9 @@ def facet_block(facet, allowed_value)
 
   def facet_link(label, value, key)
     finder_base_path = finder["base_path"]
-    link_to(label, "#{finder_base_path}?#{key}%5B%5D=#{value}", class: "govuk-link app-link")
+    view_context.link_to(label,
+                         "#{finder_base_path}?#{key}%5B%5D=#{value}",
+                         class: "govuk-link app-link")
   end
 
   def first_published_at_facet_key

app/presenters/speech_presenter.rb

@@ -39,7 +39,7 @@ def location
 
   def delivered_on
     delivered_on_date = content_item["details"]["delivered_on"]
-    content_tag(:time, display_date(delivered_on_date), datetime: delivered_on_date)
+    view_context.content_tag(:time, display_date(delivered_on_date), datetime: delivered_on_date)
   end
 
   def speech_type_explanation

app/presenters/travel_advice_presenter.rb

@@ -1,6 +1,5 @@
 class TravelAdvicePresenter < ContentItemPresenter
   include ContentItem::Parts
-  include ActionView::Helpers::TextHelper
 
   ATOM_CACHE_CONTROL_MAX_AGE = 300
 
@@ -21,7 +20,7 @@ def metadata
       "Updated" => display_date(reviewed_at || updated_at),
     }
 
-    other["Latest update"] = simple_format(latest_update) if latest_update.present?
+    other["Latest update"] = view_context.simple_format(latest_update) if latest_update.present?
 
     {
       other: other,
@@ -77,15 +76,16 @@ def alert_status
     alert_statuses = content_item["details"]["alert_status"] || []
     alert_statuses = alert_statuses.map do |alert|
       if allowed_statuses.include?(alert)
-        content_tag(:p, I18n.t("travel_advice.alert_status.#{alert}").html_safe)
+        copy = I18n.t("travel_advice.alert_status.#{alert}").html_safe
+        view_context.content_tag(:p, copy)
       end
     end
 
     alert_statuses.join("").html_safe
   end
 
   def atom_change_description
-    simple_format(HTMLEntities.new.encode(change_description, :basic, :decimal))
+    view_context.simple_format(HTMLEntities.new.encode(change_description, :basic, :decimal))
   end
 
   def atom_public_updated_at

app/presenters/unpublishing_presenter.rb

@@ -1,7 +1,7 @@
 class UnpublishingPresenter < ContentItemPresenter
   attr_reader :alternative_url, :explanation
 
-  def initialize(content_item, requested_path = nil)
+  def initialize(*args)
     super
     @explanation = content_item["details"]["explanation"]
     @alternative_url = content_item["details"]["alternative_url"]

app/services/presenter_builder.rb

@@ -1,17 +1,20 @@
 class PresenterBuilder
-  attr_reader :content_item, :content_item_path
+  attr_reader :content_item, :content_item_path, :view_context
 
-  def initialize(content_item, content_item_path)
+  def initialize(content_item, content_item_path, view_context)
     @content_item = content_item
     @content_item_path = content_item_path
+    @view_context = view_context
   end
 
   def presenter
     raise SpecialRouteReturned if special_route?
     raise RedirectRouteReturned, content_item if redirect_route?
     raise GovernmentReturned if government_content_item?
 
-    presenter_name.constantize.new(content_item, content_item_path)
+    presenter_name.constantize.new(content_item,
+                                   content_item_path,
+                                   view_context)
   end
 
 private

app/views/content_items/guide.html.erb

@@ -8,7 +8,7 @@
 
 <% unless @content_item.requesting_a_part? %>
 <script type="application/ld+json">
-  <%= raw MachineReadable::GuideFaqPageSchemaPresenter.new(@content_item).structured_data.to_json %>
+  <%= raw MachineReadable::GuideFaqPageSchemaPresenter.new(@content_item, self).structured_data.to_json %>
 </script>
 <% end %>